Frequency-modulated continuous-wave (FMCW) radar systems are widely used in collision-avoidance and adaptive cruise control systems in vehicles, which today are operating in the 76-81 GHz frequency band. In a multi-receiver system, each receive element must have a well-controlled phase response which can be calibrated over process, voltage, and temperature. Multiple receiving antennas each attached to a receiver circuit are used to provide a beamforming capability. Signals coming from a particular direction will arrive at each receiving antenna with a specific delay with respect to one another. This delay depends upon the angle of arrival of the incoming signal as well as the locations of each receiving antenna. Since the antenna locations are known, the process of determining the angle of arrival of the received radar signal is related to accurately measuring the delay of the signals among the multiple receiving elements. Furthermore, the delay can be represented as a phase shift for narrowband signals and small antenna separations. As a result, accurate determination of the phase response of each receiving element is required to accurately measure angle of arrival for the received signals. Without calibration, phase offsets can result in erroneous beamforming receiver measurements.
What is needed is a technique to adjust the phase of multiple receivers across multiple chips using a single local oscillator reference and built-in-test circuitry.